When cells are exposed to physical or chemical agents that damage DNA, deleterious effects can ensue, including mutation, cancer or death. However, mechanisms are available to repair the damage, stabilize the genome and neutralize harmful effects. During the previous funding period, focus was placed on understanding the role of human HRAD9 in processes that promote survival and genomic integrity after radiation or chemical exposure. Our studies indicate that this evolutionarily conserved gene has multiple functions needed for the cellular response to DNA damage, including cell cycle checkpoints, DNA repair and pro-apoptotic activities. Recently, we obtained evidence that HRAD9 has another important activity, which is one focus of this proposal. HRAD9 can, like p53, act as a sequence specific transcription factor. HRAD9 can bind p53 consensus sequences in the p21 promoter and cause transcription when overexpressed. In addition, we demonstrated that HRAD9 can bind the Cox-2 promoter and transactivate that gene as well. Furthermore, we show that HRAD9 is essential for the radiation induction in vivo of both p21 and Cox-2. Based on these and other functions of HRAD9, we also hypothesized a role for the encoded protein in carcinogenesis, and now provide evidence for a relationship between HRAD9 and specifically prostate cancer. These two novel HRAD9 activities, ability to regulate transcription and a role in prostate cancer, will be pursued by addressing the following two hypotheses: 1. HRAD9 is a sequence specific transcription factor that can regulate the cellular response to DNA damage by transactivation of a network of multiple downstream target genes, i.e., it controls a novel damage response regulon. Experimental aims concern structural requirements of the activity, and the identification and biological significance of inducible genes in the network. 2. HRAD9 is causally related to prostate cancer. Experiments are proposed to examine the function of HRAD9 in this type of cancer, in particular as an oncogene. The results of this study should better define the role of HRAD9 in the cellular response to DNA damage, as a novel regulator of DNA damage-inducible genes, and also elucidate the role of HRAD9 in carcinogenesis, specifically in prostate. As such, the findings focused on HRAD9 should impact on basic research as well as clinical arenas where DNA damaging agents are used for therapy and prostate cancer treatment is a concern. This proposal focuses on the role of Rad9 in regulating expression of other genes involved in controlling cell growth and maintaining stability of the genetic material. In addition, it concerns a detailed analysis of the function of Rad9 in prostate cancer. As such, this project is important since the results could impact on human health and lead to the development of novel therapeutic strategies.